In microscopic imaging, a sample plate is zoomed in by the microscope via an objective lens. There are multiple samples on the sample plate, and the sample plate needs to be moved after one sample is tested, which allows the objective lens to be aligned with another sample and zoom in the sample for imaging. When a test is performed on each of the samples, it is required to ensure that the distance between the sample plate and the objective lens is maintained to be unchanged, i.e., the working distance for imaging each of the samples is maintained to be unchanged.
However, a movable platform for mounting the sample plate has flatness error caused by machining technique itself, and flatness error also presents in mounting the movable platform to the sample plate, and the sample plate itself also has flatness error, therefore, when the sample plate moves from one sample point A to another sample point B, the issue that the point A and the point B are not in the same plane may occur, causing a difference between the imaging distance of the sample point A and the imaging distance of the sample point B, thus resulting in the situation of deviating from the best focus.
For this reason, the issue of deviating from the best focus is generally addressed by the following methods in the conventional technology.
A first method is that a microscope manufacturer improves the accuracy of machining and assembling techniques, which allows the flatness errors of the sample plate and the movable platform to be minimized, however, the improvement to the machining and assembling techniques reaches a limit, which is not easy to achieve.
A second method is that a focusing structure is provided in the microscope, and when deviation of focus occurs, an operator can fine-tune the focal length himself by experience. However, this may cause a complicated imaging operation, low efficiency, and a subjective interference to the imaging effect.
A third method is that a intelligent automatic focusing system, such as an infrared ranging system, a grating ranging system, or automatic focusing systems such as an image recognition automatic focusing system is employed, however, such systems generally contain a precise ranging system, a PLC control system, a motor drive system, an image analysis system, and etc., which results in a complicate system, high cost, and inferior stability and adaptability.
Therefore, it is required presently to provide a solution which has a simple structure, a low cost and a good stability, which address an issue of focus deviation of a sample being caused by movement of the movable platform.